Jabat al-Nursa, the al-Qaeda-linked rebel organization, together with other rebels forces have also amounted thousands of fighters for what is being called "the Great Battle of Qalamoun."
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The United Nations agency for refugees is reporting that around 1,000 families have fled from the high-stakes battle in central Syria to the Lebanese border town of Arsal, walking more than 30 kilometers (20 miles) over ridges and valleys to safety.
They are packing into wedding halls and waiting for makeshift tents as they flee the steadily intensifying fighting battle that began on Friday, said Bassel Hojeiri, former mayor of Arsal. He estimated some 10,000 people had fled to the town, saying an influx of Syrians during the past three years of conflict in that country had caused the population to nearly double.
Dana Sleiman of the UNHCR said Sunday that the families have been driven from border towns in the mountainous Qalamoun region, where Syrian forces loyal to President Bashar Assad are clashing with rebels in a drive to cut supply lines to opposition-held areas near Damascus.
She says they've been fleeing since the battle began Friday. Activists say the fighting has been intensifying. Syrian refugees have overwhelmed Lebanon since their uprising began three years ago. Lebanese officials estimate there are 1.4 million Syrians in the country, including 800,000 registered refugees.
The road to Qalamoun
A Syrian government offensive in the rugged Qalamoun hills, which stretch from Damascus to neighboring Lebanon, seeks to cut rebel supply lines to opposition-held enclaves around the capital.
Activists and analysts say the battle may be the final blow that dislodges rebels from the Damascus periphery, where food is running short and opposition fighters have lost a series of strongholds in recent weeks to forces loyal to Syrian President Bashar Assad.
On Saturday, Syrian forces went on the offensive on Saturday against rebels positioned along a major highway linking the capital with the coast, rebels said, a strategic road that is likely to be used to extract chemical weapons from the country.
The road passes through the mountainous area of Qalamoun, roughly 50 km (30 miles) north of Damascus, a region that stretches along the Lebanese border and is one of Syria's most heavily militarized districts.
Captain Islam Alloush, spokesman for the Army of Islam, the largest alliance of rebel groups in the capital, said that fighting was intense in the small highway town of Qara.
"There are a large number of our fighters stationed along the road," he said.
Diplomats say Syrian authorities have identified the road north from Damascus towards Homs and the coast as the preferred route to transport chemical agents under a US-Russian accord to eliminate them from the country's protracted civil war.
Although the army and civilians use the highway, parts of it go near rebel-held areas and convoys are prone to ambushes. The authorities have asked for equipment to help secure convoys.
Observers expect the next big battle in Syria to centre on the Qalamoun area, causing a huge exodus of refugees and stirring up anger in nearby Lebanon as Shiite Lebanese Hezbollah fighters take part in the fighting.
The Syrian Observatory for Human Rights, a UK-based monitoring group that uses a network of pro- and anti-Assad sources, said the fighting in Qara and the nearby town of Nabek was "a sign that the operation in Qalamoun has started."
Observatory head Rami Abdelrahman said that Hezbollah militants were mobilising on Saturday to fight in Qalamoun.
United Nations refugee agency spokeswoman Dana Sleiman said there were reports from the Lebanese side of the border that 600-800 refugee families had arrived from Qara at the Lebanese border village of Al-Qaa, escaping the offensive.
The Associated Press and Reuters contributed to this report
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